This invention relates to fuel compositions, and more particularly to gasoline fuel compositions, and more particularly still, to unleaded gasoline fuel compositions containing an additive to reduce the wear on non-hardened, automotive exhaust valve seats, such as exhaust valve seats composed of cast iron.
Valve recession is the process whereby the exhaust valve seats in an internal combustion, four-stroke engine are worn away by metal-to-metal contact with the valves during high speed, heavy-load conditions. As the valve seat is worn away, the valve becomes recessed in the engine head which results in loss in valve lash to the point of poor seating, valve burning and substantial power losses. If the conditions continue, severe engine damage will result which can eventually cause engine failure.
Cars subject to valve seat recession are generally limited to cars built prior to 1971. After 1971, valve and valve seats in automotive engines were hardened by a heat-treating process which eliminated the problem. Pre-1971 and many post-1971 trucks also have non-hardened seats and are subject to valve seat recession with unleaded gasolines.
For years the automotive industry has recognized that alkyl lead antiknock compounds are effective additives for preventing exhaust valve seat wear. Apparently, lead oxide coats the valve seats, lubricating and protecting these surfaces. The protection offered by lead additives is sufficient even at concentrations as low as 0.1 grams (as Pb) per gallon of fuel. However, somewhere between about 0.075 and 0.1 grams per gallon, lead additives lose their effectiveness in preventing valve recession. Thus, for operation with "unleaded" fuels (i.e., those containing no more than about 0.05 grams of lead per gallon), it can be seen that the wear on the valve seat is greater than that for leaded fuels containing 0.1 grams per gallon or more of lead. In fact, the rate of valve recession can be as much as 25 to 50 times as great, and it has been reported (in U.S. Pat. No. 3,898,055 issued to Bray) that the exhaust valves in an engine operating at full load on unleaded fuel can "sink" or recess as much as 1 to 5 mm. in only 10 hours. Obviously, such excessive wear rates cannot be tolerated, and with leaded fuels being phased out due to governmental regulations, the need for a non-leaded gasoline additive to prevent valve recession is vital.
It is, of course, known that tricresyl phosphate is somewhat effective for this purpose, as reported, for example, in U.S. Pat. No. 3,807,794 issued to Kerley et al. and in SAE Paper No. 710673 by Kent and Finnegan entitled "The Effect of Some Fuel and Operating Parameters on Exhaust Valve Seat Wear" published in 1971. However, tricresyl phosphate has one major detrimental property which has prevented its use on a commercial scale, namely, that it is extremely toxic.
It is, therefore, an object of the present invention to provide an unleaded gasoline composition containing sufficient of a relatively non-toxic additive to prevent or reduce the wear associated with unhardened exhaust valve seats of internal combustion engines.